There has been a need for improved polysulfide molding compositions which avoid the use of a lead curing agent. Use of lead curing agent presents problems of pollution and toxicity. Polysulfide molding compositions are highly useful for making molds and other molded parts.
Two-part liquid polysulfide compositions have been used which cure at room temperature within a desired working time. Such two-part liquid compositions are made by a manufacturer at one location and are sold in containers to users who then mix the two parts at another location to form the final molding composition. The molding composition then must be worked or used to make the mold within a specific time period, such as within 10-30 minutes. There must be a balance between obtaining a desired rapid cure and yet permitting the molder adequate time to work the composition and to place it in place for molding.
The compositions must result in a molded part that has good tear strength and which provide a high-strength part. On the other hand, the molding composition, upon mixing the two parts, must provide a molding composition with relatively low viscosity so that it can be placed into the mold to make the desired part. In addition, it is highly important that the two-part composition has a good storage stability, in particular it is essential that the curing agent portion is stable.
For a pourable composition, it is important that the composition formed upon mixing the two parts retains a Newtonian flow only until the composition can be put in place in the mold whereupon rapid curing occurs to provide a tough polymeric molded part. For application to vertical surfaces, a thixotropic paste-like composition is desired.
Such two-part compositions would be useful for use as pourable mold compositions which cure to a flexible rubber mold, for casting objects from gypsum plasters, waxes, Portland cements and various thermoset resins such as epoxy resins, polyesters, polyurethane and others.